Temperature compensated thermometer



Dec. 16, 1952 R. E. CLARRIDGE I 2, 1,5

TEMPERATURE COMPENSATED THERMOMETER Filed Sept. 2, 1948 r2 FIG. 2 E I2A\H g fifi i 250 ll 5 IO 5 140 E 2.10 22 E 21a g 5 I90 I2B lao g FIG. I 5E FIG. 3A 7 un 7 8 IO I7 17 l7 [6 I7 7 5 o FIG. 6A FIG. 7A

5 II II V INVENTOR. RALPH E. CLARRIDGE AH FIG. 9 FIG. 9A ATTORNEYPatented Dec. 16, 1952 TEMPERATURE COMPENSATEE THERMOMETER Ralph E.Clarridge, Rochester, N. Y., assignor to Taylor Instrument Companies,Rochester, N. Y., a corporation of New York Application September 2,1948, Serial No. 47,445

4 Claims. (01.73-368) This invention relates to thermometers and moreparticularly to glass thermometers provided with a thermcsensitivefilling medium such as mercury.

When a conventional thermometer of the mentioned type is inclosed in acase of metal or the: like, the thermometer is normally calibrated atone ambient case temperatur only. However, when the case temperaturedeviates from this value, the reading of the thermometer will not bestrictly accurate. For example, in a thermometer with a range 160 to 270R, if the end of the mercury column or other thermosensitive liquid inthe tube is located in the region of 160' F, the error due to a smallchange in case temperature will be small while if the liquid extends to270 F., the error will be larger. This is due to this greater volume ofmercury in the thermometer tube in the last assumed condition, and withthis greater volume of mercury, a rise in th case and tube temperaturewill cause a greater temperature error than in the first assumedcondition.

In accordance with the present invention, there is provided anarrangement whereby means are provided for automatically compensatingfor the errors which would otherwise be present where the thermometercase and the tube of the thermometer ar exposed to a wide range of casetemperatures.

In the drawings, Fig. 1 is a front elevation and Fig. 2 is adiagrammatic plan view of one form of thermometer in accordance with thepresent invention; Figs. 3 and 3A are views respectively illustrating afront elevation and a side elevation of a thermometer in accordance witha modified form of th invention; Fig. 4, Fig. 5, as well as Figs. 6, 6Aand Figs. 7, 7A- and 8 illustrate other modified forms of the invention,

and Fig. 9 is a fragmentary front view of a thermometer at one ambienttemperature. Fig.v 9A is a similar fragmentary front view of thethermometer at a different ambient temperature.

Referring to Figs. 1 and 2, there is disclosed a glass thermometercomprising a capillary tube 5, communicating through a capillary stem(not shown), with a bulb (also not shown) containing a filling mediumsuch as mercury 6. The thermometer is mounted in a case 1 whichterminates in a well-known protective metal bulb 8 which forms no partof the present invention. The case has mounted therein a scale plate orplates suitably graduated in degrees of temperature. As hereinillustrated, the scale plate comprises a fixed plate It) secured to thecase at the right of the tube and bearing numerals corresponding to thedegree of temperature being indicated. The other part II of the scaleplate at the left of th tube bears a calibrated scale and is movableedgewise toward and away from the tube (Fig. 2). The graduation lines donot extend perpendicular to the principal axis of the tube but areinclined slightly with respect thereto. These graduations areprogressively more inclined in passing from the lower range to th higherrange of the thermometer. It has been mentioned that the scale plate His movable edgewise toward the thermometer tube. This movement iseffected by a straight bimetallic unit I2 which is responsive to theambient temperature. As'herein illustrated, the lower end of the unit [2is secured to the case while its upper end is connected to the scaleplate ll at l3.

Let it be assumed that a thermometer of the mentioned range, namely from160 to 270 F., is calibrated with its case at F. At the ambienttemperature of 110 F, when the temperature at the bulb is 176 F, themercury column 5 in the thermometer will indicate this temperaturecorrectly as shown in Fig. 9. If, however, the ambient temperature of thcase and tube changes to F., although the temperature at the bulb isstill 176 F., there will be an increment AH in the height of the mercurycolumn due to the further expansion of the mercury in the tube, as aresult of the increased ambient tem erature. However, with the construction of the present invention, if the temperature of the case risesto 140 F., due to ambient conditions, then the bimetallic unit l2 willmove the scale plate H toward the tube, Fig. 9A, thereby increasing theeffective distance between the adjacent graduating lines, with thgreatest separation between the adjacent lines being at the upperportion of the scale plate. This compensation still causes thethermometer to indicate 176 F. in spite of the increased ambienttemperature at the case.

The modified form of the invention shown in Figs. 3 and 3A is similar tothat illustrated in Figs. 1 and 2, but differs therefrom in that theupper part of the scale plate H is mounted on the straight bimetallicunit I2A, while the lower part thereof is mounted on the straightbimetallic unit [23. These units, which are mounted on the case, arearranged in such a manner that in responding to ambient temperatures,they move the scale plate II. in the proper direction to compensate forthese temperatures.

The modified form of the invention disclosed seems in the Fig. 4 differsfrom that illustrated in Fig. 1 in that the scale plate I I is pivotedat its lower end on a pin 19 carried by the case. In this construction,when the bimetallic unit l2 responds to changes in ambient temperature,the scale II will rock toward or away from the tube 5 to compensate forambient temperature changes.

In the modified form of the invention shown in Figs. 5 and 5A, theadjustable scale plate H is moved by two coiled bimetallic elements (2Cand l2D located respectively at the upper and lower ends of the scaleplate ll, one end of each bimetallic element being fixed to the case,the other end thereof being fixed to the movable scale plate. Thus, inresponse to ambient tem-- perature changes, the movable scale plate H isautomatically adjusted in the same manner as in the construction in Fig.l, to compensate for ambient temperature errors that would otherwise bepresent.

In the modified form of the invention shown in Figs; 6, and 6A themovable scale plate H is replaced by a transparent cylinder l6surrounding the tube 50f the thermometer. The thermometer tube ispreferably located close to the inside surface of the back of thecylinder "i (Fig. 6A) and the front surface of the cylinder is providedwith graduating lines arranged in a manner similar to those on the scaleplate illustrated in Fig, 1. In thisfform of the invention, a bimetalliccoil 12E (Fig. 8) having its ends respectively connected to the case 1and to the cylinder 1 6, is responsive to the ambient temperatures torotate the cylinder in order to bring difierent portions of graduationsinto reading relation to the thermometer tube. Suitable rollers i-lcarried by the case -'1 guide the lowerend of the cylinder 15.

The modified form of the invention shown in Figs. '7 and 7A differs fromthe form shown in Figs. 6 and 6A, in that the thermometer tube 5 islocated outside of the cylinder 16 7A). in the space between thecylinder and the fixed scale plate {0, In this modification also, thebimetallic coil 1213 is efiective to rotate the cylinder I6 to bringdifierent portions of the-graduated lines thereon into reading relationwith the thermometer tube 5.

What I claim is:

i. In a thermometer including a glass tube communicating with abulbcontaining a thermosensitive liquid and a case provided with a scaleplate in cooperative relation with said tube, said plate havinggraduation lines extending in a direction transversely of said tub Saidlines being progressively more inclined with respect to the main axis ofthe tube from the lower end of the temperature range on thescale plateto the high end of said range, and means including a, bimetallictemperature responsive strip located at said case for moving said scaleplate in a direction generally at right angles to the main axis of saidtube whereby the efiect of changes in temperature at the case will becompensated for .in the readings of the thermometer.

2. A thermometer including a straight glass capillary tube communicatingwith a bulb con- 4 taining a thermosensitive liquid and a scale plate incooperative relation with said tube, said scale plate having graduationmarks thereon along said tube related to the height of the liquid in thetube, said graduation marks extending in a direction to intersect themain axis of the tube and having portions with equal spaces betweenadjacent portions effective at a given ambient temperature at the scalefor indicating the temperature at the bulb, the remaining portions ofsaid graduation marks defining spacing between adjacent marks whichchanges from one end of the scale to the other, temperature responsivemechanism located at said case and means including said mechanism forcausing relative movement between the tube and the scale plate inresponse to ambient temperature changes at said scale plate.

3. In a thermometer including a lass tube communicating with a bulbcontaining a thermosensitive liquid and a case provided with a scaleplate in cooperative relation with said tube, said plate havinggraduation lines extending in a direction transversely of said tube,said lines being progressively more inclined with respect to the mainaxis of the tube from the lower end of the temperature range on thescale plate to the high end of said range, and temperature responsivemeans located at said case for cheating relative movement between saidscale plate and said tube in a direction at right angles to the mainaxis of said tube whereby the effect of changes in temperature at thecase will be compensated for in the readings of the thermometer.

4. In athermometer including a lass capillary tube communicating with abulb containing a thermosensitiveliquid and a scale member incooperative relation with said tube, said member having graduation marksthereon related to the height of the liquid in the tube,- said memberbe.- ing adjustable to vary the effective indicating spacing betweenadjacent graduation marks, mechanism located at said scale andresponsive to ambient temperatures thereat, said mechanism beingconnected to adjust said member to vary the effective indicating spacingbetween adjacent graduation marks from the low temperature end of therange on said scale plate to the high temperature end of said range inresponse to an increase in ambient temperature at said scale.

RALPH E. 'CLARRIDGE.

REFERENCES CITED The following references are of record in the file ofthis patent:

Y UNITED STATES PATENTS Number Name Date 739,967 Wohl et al Sept. 20,1903 1,712,653 Eglo-fi May 14, 1929 2,l l3,'-I75 Hertel Jan. 10, 19392,293,064. Kahn Aug. 18, 1942 FOREIGN PATENTS Number Country Date445,626 Great Britain Apr. 16, 1936 653 0 Germany e.. Dec. 17, 1936

